But have these collective announcements ended the global warming debates? No, stay tuned for further developments.

Cyclical, abrupt, and dramatic global and regional temperature fluctuations have occurred in observable patterns over millions of years, long before humans invented agriculture, capitalism, smokestacks, and carbon trading schemes. To appreciate just how lucky we are to live in the present, consider climate cycles from a historical perspective. Over the past 400,000 years, much of the Northern Hemisphere has been covered by ice up to three miles thick, at regular intervals lasting about 100,000 years each. Very brief interglacial cycles lasting about 12,000 to 18,000 years, like our current one, have offered reprieves from the bitter cold. From this perspective, there can be no doubt that current temperatures are abnormally warm.

The average temperature of our planet has been gradually increasing on a fairly constant basis over the past 18,000 years or so since it began thawing out of the last ice age. About 12,000 to 15,000 years ago, the Earth had warmed enough to halt the advance of the glaciers and cause sea levels to rise. About 8,000 years ago, a land bridge across the Bering Strait submerged, cutting off migrations of people and animals to North America.

As recently as 1,000 years ago, from about 800 to 1300, much of the world climate was similar to what it is now, but Greenland was warmer. Icelandic Vikings began to settle on Greenland’s southwestern coast in the 980s and raised cattle, sheep, and goats in the grasslands. Then around 1200, temperatures began to drop, causing settlements to be abandoned by 1350 or so. Atlantic pack ice began to grow around 1250, and shortened growing seasons and unreliable weather patterns, including torrential rains in northern Europe, led to the Great Famine of 1315-17.

Although the last 500 years have been generally mild, substantial climate fluctuations have occurred. An example is the Little Ice Age (which was not a true ice age) that brought frigid weather to the Northern Hemisphere between the 16th and 19th centuries. By the mid-17th century, alpine glaciers in Switzerland advanced to gradually engulf farms and villages. The Thames River and New York Harbor froze over by 1780, and sea ice closed shipping harbors in Iceland, where an estimated one-third of the population perished.

In about 1850, the northern climate began to warm again, although slight cooling recorded at certain ground stations in the 1970s prompted some media attention regarding a possible imminent ice age. Then, little more than a decade later, alarm was trumpeted in the press. Global warming was now an impending menace, and human-produced CO2 from fossil-fuel burning industries was indicted as its villainous agent.

Forcing the Issues

It is currently impossible to reliably forecast weather events over days and weeks, much less climate changes measured over decades. The variables are too numerous, and their interactions are too complex and dynamic, to support accurate long-term modeling. Many factors, and clearly the most dominant ones, involve naturally occurring events. Key among these is believed to be changes in the Earth’s orbital eccentricity around the sun, along with its slow axial “wobble” over many thousands of years. These conditions influence the amount of sunlight received on the surface and seem to correspond with glacial and interglacial cycles. Short fluctuations within interglacials appear to be linked to other influences. They include periodic cyclical variations in solar outputs, seasonal effects of cloud cover, precipitation and vegetation growth, and occasional volcanic eruptions producing warming greenhouse gases along with dust and aerosols that block sunlight to cause cooling.

Many scientists believe that Pacific Decadal Oscillation and Atlantic Multidecadal Oscillation cycles associated with El Niño and La Niña conditions in combination with solar activity variances have had important climate influences during the past century. These factors may account for much of the observed warming trends of 1910-39, cooling from the 1940s to the ’70s, and warming during the ’80s and ’90s. Solar activity cycles of about 11 years and 200 years may modulate the effects of galactic cosmic ray magnetic fields, producing changes in cloud cover with both warming and cooling results.

Based upon current solar data, the Russian Pulkovo Observatory concludes that Earth has passed its latest warming cycle, and predicts that a fairly cold period will set in by 2012. Temperatures may drop much lower by 2041, and remain very cold for 50 to 60 years. Kenneth Tapping at Canada’s National Research Council thinks we may be in for an even longer cold spell. He predicts that the sun’s unusually quiet current 11-year cycle might signal the beginning of a new “Maunder Minimum” cold period, which occurs every couple of centuries and can last a century or more. Then again, theories are only theoretical.

The Intergovernmental Panel on Climate Change (I.P.C.C.), established in 1988 by two United Nations organizations, the World Meteorological Organization and the U.N. Environmental Program, put the global warming issue and purported human (anthropogenic) influences through fossil burning on center stage. Its working groups and a task force review published scientific and technical literature, but do not conduct original research. Reports widely circulated as authoritative appear in government, media, and blog discussions. Of these, “Summary for Policymakers” reports are by far the most influential and draw the most attention, because they are non-technical and provide sound-bite conclusions that media organizations favor, particularly if they are exciting and alarming.

The third summary report released in 2001 produced a great deal of headline material. It concluded that there was new and stronger evidence that most of the warming observed over the past 50 years is attributable to human activities; and that human influences will continue to change atmospheric composition throughout the 21st century, with global temperatures and sea levels projected to rise in all scenarios. A fourth report released in 2007 contained many of the same observations, including a highly disputed and actively challenged “hockey stick” graph that directly correlated warming with increasing atmospheric carbon dioxide concentrations commencing with the industrial revolution. The same full-color graph had appeared six times in the previous 2001 report.

Many questions remain to be answered regarding the real significance of anthropogenic carbon dioxide as a climate forcing factor and related rising sea level consequences projected by the I.P.C.C. First, there is no incontrovertible evidence to support contentions that pre-industrial carbon dioxide levels were consistently lower than the 380 ppm recorded now. More than 90,000 published measurements carried out between 1812 and 1961 indicate that atmospheric levels were actually rising before the Industrial Revolution. They reached about 440 ppm in 1820, dropped to about 390 ppm by 1855, and rose back to about 440 ppm by 1940.

Cause and effect relationships between atmospheric carbon dioxide concentrations from all sources and global temperatures are inconclusive. Although carbon dioxide levels have generally been observed to increase during warm periods and fall during colder ones, the temperature changes typically lead rather than follow carbon dioxide changes. For example, records indicate that carbon dioxide concentrations fall at the start of ice ages, when more of the gas is absorbed by colder oceans, and levels rise during glacial retreats when the processes reverse.

Carbon dioxide is broadly presented as the major greenhouse gas, and fossil burning as its dominant source. In reality, carbon dioxide comprises only a very tiny amount of total atmospheric gas content, less than 4/100ths of 1 percent. The National Oceanographic and Atmospheric Administration estimates that about 97 percent of that small amount originates from natural sources, and further, that all atmospheric carbon dioxide may account for less than 10 percent of total greenhouse influence. In comparison, water vapor, by far the primary greenhouse gas, may account for 70 percent or more of the very small total warming effect.

While indicating that climate models are getting better, the I.P.C.C. has acknowledged that predictive capabilities are fallible, stating that: “Such models cannot yet simulate all aspects of climate (e.g., they cannot account for the observed trend in surface-troposphere temperature changes since 1979) and there are particular uncertainties associated with clouds and their interaction with radiation and aerosols.”

Clouds are comprised mostly of water droplets (not greenhouse gases) and are known to produce important complex warming and cooling effects. Current models have limited abilities to analyze feedbacks between clouds, water vapor, and reflective contributions of snow cover; the physics of the ways various cloud altitudes moisturize the atmosphere; and dynamic influences of convection. Interestingly, NASA satellite measurements of global surface and ocean precipitation done between 1979 and 2004 have revealed no added net atmospheric water vapor concentrations due to climate warming evaporation effects that were predicted by previous models.

The I.P.C.C.’s predictions of potentially catastrophic sea level increases caused by Arctic and Antarctic melts may also warrant serious reassessments. More than a decade of satellite altimeter measurements of ice mass changes in Greenland and Antarctica suggests less reason for alarm. Annual Greenland ice sheet thinning at the margins (about -42 gigatons, or GT, of water mass) appears to be more than balanced by inland mass increases for a +11 GT gain, due to increased snowfall. During a similar period, the western Antarctica Ice Shelf has lost about -47 GT per year, while the Eastern Ice Shelf has gained mass by about +16 GT per year. The Greenland and Antarctic water mass changes together are estimated to yield a net sea level increase of about 0.05 mm per year. At this rate it would require about 1,000 years to raise the global sea level by only 5 cm, and 20,000 years to raise it one meter.

Some I.P.C.C. study participants and reviewers have questioned the objectivity of its conclusions. For example, a press conference release linking hurricanes to global warming following the devastating U.S. 2005 storm season was not supported by known research, but it dominated world news headlines. Subsequent hurricane seasons have been relatively quiet.

Strongly influenced by the first three I.P.C.C. reports, the Kyoto Protocol was established under the U.N.’s Framework Convention on Climate Change in 2005, following ratification by Russia. Its terms required participating industrialized nations to reduce emissions of carbon dioxide and five other greenhouse gases (G.H.G.s) to 5.2 percent below 1990 levels by 2012, but provided exemptions for China and India. It also allowed the E.U. and Russia to trade G.H.G. emission credits within regional countries, allowances that were not extended to the U.S.

Neither the Clinton nor the Bush Administration found Protocol terms acceptable. These decisions have followed a policy established through unanimous passage of the bi-partisan 1997 Byrd-Hagel Senate Resolution, which stated that the U.S. should not be signatory to any protocol that does not include binding timetables for both developing and industrialized nations, or that “would result in serious harm to the economy of the United States.”

Although Vice President Al Gore symbolically signed the Protocol, President Clinton never submitted it for ratification to the Senate, where critics argued that it offered unfair economic advantage to other nations. A return to a 1990 time reference, along with emission trading credits, would benefit Germany following the reunification that eliminated many dirty East German industries, similar to Russia’s situation after the U.S.S.R. collapse. The U.K. would also gain an advantage following the discovery of an enormous North Sea natural gas deposit that enabled a major coal phase-out. China, which is exempt, has become an industrial giant and by some estimates is the world’s biggest G.H.G. generator.

Republican presidential candidate John McCain favors an alliance with Europe to create a successor to the Kyoto Protocol that would not exempt China and India. He and Senator Joe Lieberman co-sponsored Senate legislation in 2003, 2005, and 2007 that would mandate greenhouse gas emission reductions. The most recent proposal would require G.H.G. reductions from utilities and industrial, commercial, and transportation sectors (about 85 percent of the U.S. economy) to 2004 levels by 2012; then downward to less than a third of that by 2050. He also supports cap-and-trade programs as the best approach.

Al Gore continues to promote carbon emission credit trading through a London-based hedge fund called Generation Investment Management, which he co-founded with David Blood, former head of investment management at Goldman Sachs. Goldman Sachs is also a large shareholder in the Chicago Climate Exchange created in 2003 as a “voluntary pilot agency” to advance trading in U.S. carbon emissions. Both organizations are working to persuade governments to block new power plants that use fossil fuels. The result will be lower carbon emissions, and better market trading of scarce allowances. Viewing carbon as a new commodity, Gore told members at a March 2007 Joint House Hearing of the Energy and Science Committee: “As soon as carbon has a price, you’re going to see a wave [of investment] in it…there will be unchained investment.”

But who will benefit from the investment? Will huge burdens on the economy and high costs transferred to consumers help hold sea levels in check or save polar bears? Or is it just possible that global warming hysteria is being exploited to cook the books in favor of hedge fund operators, speculators, and more subsidies for non-competitive energy interests? If so, maybe Mother Nature will soon set the records straight.

Larry Bell is a professor of architecture and an endowed professor of space architecture at the University of Houston and directs the Sasakawa International Center for Space Architecture. This is the first of three articles on current energy and environmental issues.